“…This cannot be the case, however, for the same phenomenon is exhibited in He atmospheres. Veljby (15) shows that it also occurs in air if the light is turned off just after the initial uptake of CO9 while the rate of photosynthetic assimilation is still low. We have also observed it with leaves in air and 4 % CO2 at O°C where the steadystate rate of photosynthesis is suppressed.…”